I'm presuming his plugin has its own CSS file, which is where line 103 is located. Since the plugin would likely load its CSS after anything we'd load, the !important part of the plugin's CSS on line 103 is going to override anything previously loaded.

I'd ask him if it's okay to modify line 103 in the plugin's CSS file. If he says yes, just modify the plugin directly.

The style.css file from the HTML5 JQuery Audio Player Pro plugin doesn't have a .rightdiv property on line 103, there s a right div in that file, but it's already set for 283px width and isn't marked !important. I tried looking in the various Pagelines framework css files, but couldn't find any line 103 .rightdiv instances.

Unfortunately, since the source of the CSS is a premium 3rd party plugin, I wouldn't know how to support this. It's really up to the developer. As you point out, you cannot even match the corresponding CSS element to the line cited by the developer, so I'm presuming something is incorrect.